1) The hormone contained in the birth control pill can act to delay or prevent ovulation. Since conception sometimes takes place a day or two after the act, if the pill is taken after the act but before ovulation and it successfully prevents ovulation then a pregancy can be prevented before it occurs.
2)The hormone can also irritate or thin the lining of the uterus, the preventing implantation of a fertilized embryo. Depending on one's definition of whether the pregnancy begins at conception or implantation, this could constitute an abortion.
I don't claim to have detailed medical expertise, but because of the precise timing requirements for #1 to occur, I have to believe that #2 is the more common mode of operation for the 'morning after' pill.
No. It can take a good month for the cumulative effect of the birth control pills to set in and prevent ovulation. When used after sex as a birth control, there is nothing the hormones can do to stop a ripening follicle at that point.
Your #2 was correct.